Conventional fuel injection systems for internal combustion engines may include one high-pressure fuel pump for supplying a predetermined amount of fuel at a high pressure to injection nozzles within a fuel injection system. Depending on the type of engine and its rated power, more than one high-pressure fuel pump may be provided for delivering a sufficient amount of fuel at a high pressure to the engine, in particular a diesel engine, operating at a desired load.
The high-pressure fuel pumps may be driven directly by the internal combustion engine. In such an arrangement it may not be possible to shut-off the fuel pumps during operation. However, the amount of fuel supplied to the pumping elements of the fuel pumps can be adjusted via flow control valves. An engine control module (ECM), or more generally a control unit, may be provided for controlling the flow control valves.
It is known that a high-pressure fuel pump may have a pumping unit or several pumping elements in which fuel leakage can occur. Fuel leakage may occur for example in a piston pump between a piston and a piston guide. The fuel leaked from the pumping element will not be pumped into the high-pressure distribution line system. Typically, the fuel leaking from the pumping element and not being pumped is recycled to an intake section of the high-pressure fuel pump. Due to the recycling of the fuel leaked from the pumping element, heat is generated in accordance with the pressure and the amount of fuel leaked from the pumping element, which heats the fuel and the parts of the high-pressure fuel pump that are contacted by or are near this fuel.
As long as a high-pressure fuel pump pumps a sufficient amount of fuel for operating the internal combustion engine in a normal pump mode, the heating may not actually cause a problem because, in addition to the heated, leaked fuel, new fuel having a lower temperature is supplied from a fuel tank, such that the mixture of the leaked fuel and the new fuel will have a temperature below a critical limit. However, the situation may become critical if the internal combustion engine is operated at an idling speed or at a low load with a corresponding low fuel consumption for too long of a time period. In this case, the ratio between the leaked fuel and the amount of new fuel supplied is relatively large and, consequently, the temperature of this mixture may rise. Further, the temperature of the parts of the high-pressure fuel pump contacted by this mixture will increase, because the portion of fuel leaked from the pumping element is relatively high in comparison to the portion of the new fuel from the tank having the lower temperature. Consequently, parts of the high-pressure fuel pump may heat up to a temperature at which damage can occur.
In DE 195 01 475 A1 a fuel injection system for an internal combustion engine comprises one fuel pump. It is stated that the heating of fuel in such a fuel injection system might be a problem. In this disclosure, the fuel pump is driven by the internal combustion engine. For avoiding an undesired heating of fuel within the fuel injection system, it is proposed to provide a coupling between the internal combustion engine and the fuel pump. A control unit is connected with the coupling such that, upon actuating, the coupling pressure generated by the fuel pump can be adjusted to the injection pressure. It is indicated that the disclosed arrangement eliminates an undesired heating of the fuel in the section of the pressure piping leading to the injection valves, because the energy supplied by the internal combustion engine for the fuel pump is only used as necessary for generating the necessary injection pressure. The remaining energy is dissipated into the coupling. This known arrangement requires a coupling and a control unit for such a coupling.
In EP 1 167 731 A2 a method for monitoring the operation of the pump function for vehicles having at least two electrical fuel pumps is disclosed. It is mentioned therein that, in case one of the fuel pumps fails, the other fuel pump may pump an amount of fuel up to a maximum. However, if the internal combustion engine should be operated at full load, a pressure drop may occur at the working fuel pump. Consequently, a temperature increase may occur, which in turn might damage parts, e.g. the catalytic converter or the exhaust manifold. For this reason, a method for monitoring the operation of the pumps is proposed in which the fuel pumps are alternatively operated. The output rate of each fuel pump is determined and compared with set-points. An operational point for the engine is selected, at which the power of the selected, active fuel pump is just sufficient to supply the engine fuel demand. Thus, this method can identify a faulty fuel pump, i.e. by determining that its output rate is lower than a corresponding set-point. Therefore, this known method does not avoid an increase of temperature, but rather it stops a faulty fuel pump from operating and possible being damaged.
For the sake of completeness, the following documents are mentioned. EP 0 204 981 A2 (corresponding to U.S. Pat. No. 4,726,335) refers to an arrangement including two fuel pumps. In a first operation mode, both fuel pumps supply fuel. In a second operation mode, only one of these fuel pumps is supplying fuel, the other fuel pump is turned off. Which fuel pump is being turned off is randomly selected. In a third pump operation, both pumps are being driven in a reverse direction to suck fuel instead of supplying fuel.
WO 2005/106239 A1 refers to a fuel supply apparatus for an internal combustion engine including two low-pressure pumps and one high-pressure pump. In a first operation mode, the first low-pressure pump is activated, the second low-pressure pump is not activated. The first operation mode is chosen in case fuel is supplied solely by the low-pressure fuel supply means. Accordingly, in the first operation mode the high-pressure pump is also turned off. In a second operation mode, the first and second low-pressure pumps are not driven, but the high-pressure pump is supplying fuel. Due to this arrangement pulsation generated from the high-pressure pump should not propagate to the low-pressure fuel system.
JP 03-074564 refers to a fuel supply system including two fuel pumps. These pumps are driven alternately to prevent discharge of vapor in the fuel.
Finally, WO 2007/135545 A1 refers to a fuel pump system adapted to be used for different kind of fuels.
The present disclosure is directed to overcoming or alleviating one or more of the problems set forth above.